1. Field of the Invention
The present invention relates to a power management system and, more particularly, to a power management system which manages the power consumption of client computers in a corporation.
2. Description of the Related Art
The power demand varies depending on factors such as the season, weather, and the like, and a power company must come up with power equipment that can cope with the peak power demand. Therefore, when the power load varies abruptly, the power efficiency in a power plant deteriorates.
To solve such problems, a technique for demanding power savings from the power company to commercial-scale utility customers, and leveling the load variation of the power demand is known. As an example of such technique, an electronic device is known which attains a peak power shift of a commercial power supply in such a manner that it receives electric power from a battery supply in place of an AC adapter, and without charging the battery supply, in a time band designated by the user.
Also, the following technique is available. That is, if a given corporation reduces power consumption the request of a power company, the power company pays an incentive fee corresponding to the reduction power. For example, a corporation decreases consumption power in a time band corresponding to a peak power demand such as an afternoon in midsummer, and reduces the cost to the whole corporation (Jpn. Pat. Appln. KOKAI Publication No. 2002-176729).
However, in the technique for saving electricity in a time band designated by the user, since power consumption of a commercial AC power supply is reduced in a given time band and battery charging is done in another time band irrespective of the actual power supply-demand relationship, a peak shift that reflects actual power supply cannot be attained. For example, when a given device is set to be driven by a battery in a predetermined time band in an afternoon in summer, even when the power supply-demand relationship is relaxed owing, for example, to rain or unseasonable weather, an unnecessary peak shift is still automatically made.
With this technique, since a plurality of users simultaneously reduce power consumption, the power supply-demand balance changes abruptly, and such change adversely influences safety reliability of the power management system. As another problem, the battery-driven time is limited.
Especially, when it is planned to manage a peak power shift without making users realize it, most of the charged battery is used during the peak power shift period. Hence, when a long peak shift operation time band is adopted, the peak shift function works in the former half of that time band, but the peak shift effect is considerably reduced in the latter half of the time band.
In the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-176729, the fundamental advantage of using electricity is offset as a result of power savings. For example, the above technique is subjected to the disadvantage that the air conditioning temperature of a building is set higher than what is generally considered comfortable.